1. Field of the Invention
The present invention relates to a method of separating a polycyclic diol by distillation from a mixture containing the polycyclic diol and at least one aldehyde compound as impurity.
2. Description of the Prior Art
Commercially available polycyclic diols, for example, tricyclo[5.2.1.02,6]decane dimethanol (TCDDM) represented by the following formula: 
usually contains aldehyde intermediates such as 
as impurities in a proportion of 3875 to 8000 ppm in terms of carbonyl in the aldehyde impurities. To purify TCDDM to an aldehyde impurity content corresponding to 2500 ppm carbonyl or lower, conventionally employed is a method wherein TCDDM is dissolved in an organic solvent such as alcohol, catalytically hydrogenated in the presence of a catalyst, and then distilled. However, this method requires an additional step of catalytic hydrogenation, necessitates the use and recovery of the organic solvent, and is likely to by-produce other impurities, thereby being disadvantageous economically.
As described above, commercially available polycyclic diols contain aldehyde compounds (precursors or intermediates of the polycyclic diols) as impurities. Since the boiling points of these aldehyde compounds are close to those of the polycyclic diols, the aldehyde compounds cannot be effectively removed from the polycyclic diols by usual distillation methods. In addition, since the aldehyde compounds are highly reactive, the remaining aldehyde compounds cause coloration or yellowness during an ester-interchange polymerization using the polycyclic diols as a monomer component.
As a result of extensive study in view of developing a method of purifying the polycyclic diol by distillation, the inventors have found that the aldehyde compound impurities can be effectively removed by distilling the polycyclic diol in the presence of 200 to 5000 ppm of an alkali metal compound and/or an alkaline earth metal compound. The present invention has been accomplished on the basis of this finding.
Thus, the present invention provide a method of purifying a polycyclic diol, which comprises distilling a mixture of the polycyclic diol and at least one aldehyde compound as impurity in the presence of an alkali metal compound and/or an alkaline earth compound in a proportion of 200 to 5000 ppm based on the polycyclic diol, thereby removing the aldehyde compound from the polycyclic diol.
The distillation of the polycyclic diol of the present invention will be described below in more detail.
The purifying method of the present invention is characterized by distilling a crude polycyclic diol containing at least one aldehyde compound as impurities in the presence of 200 to 5000 ppm of an alkali metal compound and/or an alkaline earth metal compound, thereby efficiently removing the aldehyde compound impurities from the polycyclic diol.
The polycyclic diol referred to in the present invention is tricyclodecane dimethanol, bicycloheptane dimetanol, decalin dimethanol, pentacyclopentadecane dimethanol, norbornene dimethanol, etc., and particularly, 3,8-bis(hydroxymethyl)-tricyclo[5.2.1.02,6]decane and 4,9-bis (hydroxymethyl)-tricyclo[5.2.1.02,6]decane.
The alkali metal compound usable in the present invention may include sodium hydroxide, potassium hydroxide, cesium hydroxide, lithium hydroxide, sodium hydrogen carbonate, sodium carbonate, potassium carbonate, cesium carbonate, lithium carbonate, sodium acetate, potassium acetate, cesium acetate, lithium acetate, sodium stearate, potassium stearate, cesium stearate, lithium stearate, sodium borohydride, sodium phenylborate, sodium benzoate, potassium benzoate, cesium benzoate, lithium benzoate, disodium hydrogenphosphate, dipotassium hydrogenphosphate, dilithium hydrogenphosphate, disodium phenylphosphate, disodium salt of bisphenol A, dipotassium salt of bisphenol A, dicesium salt of bisphenol A, dilithium salt of bisphenol A, sodium phenolate, potassium phenolate, cesium phenolate, lithium phenolate, etc. Particularly preferred is potassium hydroxide.
The alkaline earth metal compound usable in the present invention may include magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, magnesium hydrogen carbonate, calcium hydrogen carbonate, strontium hydrogen carbonate, barium hydrogen carbonate, magnesium acetate, calcium acetate, strontium acetate, barium acetate, magnesium stearate, calcium stearate, calcium benzoate, and magnesium phenylphosphate.
These alkali metal compound and/or the alkaline earth metal compound may be used alone or in combination of two or more in the form of solid or solution in water or a lower alcohol such as methanol and ethanol, or a mixture thereof. The concentration of the solution is not specifically limited. The use amount of the alkali metal compound and/or the alkaline earth metal compound is 200 to 5000 ppm, preferably 500 to 2000 ppm in total based on the polycyclic diol.
The distillation of the polycyclic diol containing the aldehyde impurities is conducted as described below, although not strictly limited thereto.
A solid alkali metal compound and/or alkaline earth metal compound, or an aqueous or alcohol solution thereof having a concentration of 1 to 30% by weight is dissolved in the polycyclic diol in a proportion of 200 to 5000 ppm based on the polycyclic diol. The resultant solution is distilled at 180 to 230xc2x0 C. under a reduced pressure of 0.1 to 15 mmHg. It is preferred to discard the initial distillate (about 5 to 20% of the solution being distilled) and collect the subsequent main distillate (about 80 to 95% of the solution being distilled) as the purified polycyclic diol. The aldehyde concentration in the polycyclic diol purified by the method of the present invention is lower than the detection limit, i.e., 25 ppm in terms of carbonyl group.
The purified polycyclic diol thus obtained is preferably used as a diol component for producing various polymer, particularly polycarbonate, with less yellowing.
The present invention will be explained in more detail by reference to the following example which should not be construed to limit the scope of the present invention.
The content of the aldehyde impurities (carbonyl content) in the polycyclic diol was determined by absorption spectrophotometry of a hydrazone derived from the reaction of 2,4-dinitrophenylhydrazine and the carbonyl of the aldehyde impurities according to the following reaction scheme. 
1. Preparation of Reagents
Into 500 mL of guaranteed methanol, were added about 5 g of 2,4-dinitrophenylhydrazine and several drops of concentrated hydrochloric acid. After boiling the methanol mixture for two hours, methanol was subjected to fractional distillation. The collected fraction was sealed and stored in a refrigerator.
2,4-Dinitrophenylhydrazine was purified twice by recrystallization from the carbonyl-free methanol. The obtained crystals were vacuum-dried and stored in a refrigerator while shielding them from light by aluminum foil. DNP saturated solution
Into a 100-mL ground stopper Erlenmeyer flask, were placed 0.165 g of DNP and 50 mL of MeOH. The contents were heated over a water bath of 50xc2x0 C. for 30 min under stirring, allowed to stand at room temperature for at least one hour for cooling, and filtered through a 5A filter paper. The solution was prepared just prior to its use and kept shielded against light by aluminum foil.
KOH placed in a polymer bottle was diluted with deionized water.
2. Absorption Spectrophotometry
After accurately weighing a sample TCDDM (40 to 42 mg) into a screwed test tube, 1 mL of the carbonyl-free methanol (MeOH) was added thereinto.
After completely dissolved, 1 mL of DNP saturated solution and two drops of hydrochloric acid were further added, and the test tube was shaken for 10 sec.
After tightly sealing, the test tube was heated at 100xc2x0 C. in a drier for five minutes, shaken for 10 sec, and then allowed to stand for 30 min. After cooled to room temperature, 5 mL of MeOH were added to the test tube, which was further shaken for 10 sec.
Then, 4 mL of 10 wt % KOH solution were added to the test tube, which was shaken for 60 sec, thereby preparing a sample solution for absorption spectrophotometry. A solution for blank test was prepared in the same manner as above except for omitting TCDDM.
After allowing each sample solution to stand for 1 hr to 1.5 hr to stabilize the color development, the absorbancy of each sample solution was measured in the range of 400 to 650 nm.
The measured results were calibrated by a calibration curve obtained using benzaldehyde, thereby calculating the content of aldehyde impurities (carbonyl content) in the sample PCDDM.